1. Field of the Invention
The present invention relates to an earth fault detection circuit and a power source device including the same.
2. Description of the Related Art
In general, a power source device for controlling power source supply from a high-voltage battery to a load is connected to the high-voltage battery which is mounted in a vehicle such as an electric car, a fuel-cell car or a hybrid car. The power source device is insulated from a car body. Thus, in response to the risk of electrical shock becoming high when an earth fault occurs in the power source device, a circuit for detecting an earth fault in the power source device is proposed.
An inverter for drive-controlling a motor can be connected to the high-voltage power source as a load. In such a case, even when the earth fault in the high-voltage power source is to be detected, it becomes difficult to make a correct judgment about the earth fault since, under the influence of a noise which is generated from the inverter during the operation of the motor, the noise is superimposed on a detection signal. To cope with this, an earth fault detecting device is known as an earth fault judging means that takes the influence of such a noise into consideration. For example, JP-2006-177840-A describes such an earth fault detecting device, which includes an external noise removing circuit in which a high-frequency noise removing function can be turned ON/OFF by a switch circuit. Thus, the earth fault detecting device judges presence or absence of generation of the earth fault based on a response waveform appearing when a pulse signal is applied to one end side of a high-voltage power source through a coupling capacitor in a state in which the high-frequency noise removing function is held in an ON state.